Save meta to local file have an error when import_meta_graph

[pepure]

When I freeze ckpt and meta to PB model，I meet this error ，so I test tf.NET Examples to debug problem。
Test code as follows： https://github.com/SciSharp/TensorFlow.NET-Examples/blob/master/src/TensorFlowNET.Examples/ImageProcessing/DigitRecognitionCNN.cs

after train finish, I add some code to save graph and constant into local "ckpt" "meta" files,like this:


then I get these files in debug folder：

Then I use "tf.train.import_meta_graph("\MNIST.meta");" to load meta,some error occurs ,like this:

I test other people's meta files ,all is load OK . So I think maybe "saver.save(sess, "MNIST");" code has some bugs . Please help me ,Thank you very much ~